Vehicles include a number of different components and assemblies that have an illuminator and/or a signal lamp associated therewith. Great interest has been shown in the use of electroluminescent semiconductor devices, such as light emitting diodes (LEDs), as illuminators and signal indicators because they offer many potential advantages as compared to other conventional low voltage light sources. Other light sources suffer from many deficiencies, including: they are relatively inefficient, such as conventional tungsten incandescent lamps; require high voltages to operate, such as fluorescent and gas discharge lamps; or are susceptible to damage, such as incandescent lamps. Accordingly, these alternate light sources are not optimal for vehicular applications where only limited power or low voltage is available, or where high voltage is unacceptable for safety reasons, or in applications where there is significant shock or vibration. LEDs, on the other hand, are highly shock resistant, and therefore provide significant advantages over incandescent and fluorescent bulbs, which can shatter when subjected to mechanical or thermal shock. LEDs also possess operating lifetimes from 200,000 hours to 1,000,000 hours, as compared to the typical 1,000 to 2,000 hours for incandescent lamps or 5,000 to 10,000 hours for fluorescent lamps.
Because of these and other advantages, LEDs have become common in a wide variety of opto-electronic applications. Visible LEDs of all colors, including white, are used as status indicators within instrument panels and consoles in cars, trucks, buses, minivans, sport utility vehicles, aircraft, and the like. In each of these applications, the low intensity luminous flux emitted by the LEDs limits the relative visibility of the indicator, particularly in high ambient lighting conditions.
High intensity amber, red, and red-orange emitting visible LEDs are used in integrated arrays of visual signaling systems such as vehicle CHMSLs (center high mounted stop lamps), brake lamps, exterior turn signals and hazard flashers, exterior signaling mirrors, and the like. In each of these applications, the limited luminous flux emitted by the individual discrete LEDs within the array requires the simultaneous operation of eight or more discrete LEDs in order to achieve the desired beam intensity and distribution.
Multi-color combinations of pluralities of high intensity visible colored LEDs are being used as the source of projected white light for illumination purposes. Such illuminators are useful as vehicle or aircraft map lights, for example, or as vehicle or aircraft reading or courtesy lights, cargo lights, license plate illuminators, back-up lights, and exterior mirror puddle lights. Phosphor-enhanced “white” LEDs may also be used in some of these instances as illuminators. In these illuminator applications, where high beam intensity is critical to production of effective projected illumination, the limited luminous flux emitted by the individual discrete LEDs requires the simultaneous operation of many discrete LEDs in order to achieve desired beam intensity, color, and distribution.
Infrared (IR) emitting LEDs are being used for remote control and communication in such devices as VCRs, TVs, DVD players, CD players, and other audio-visual remote control units. Similarly, high intensity IR emitting LEDs are being used for communication between IRDA devices such as desktop, laptop, and palmtop computers, personal digital assistants (PDAs), and peripherals such as printers, network adaptors, pointing devices (“mice,” “trackballs”, etc.), keyboards, and the like. Signal range and quality are dependent on the magnitude of flux generated by the LED emitter, and the limited flux has had a detrimental impact on performance of these existing IR transmitters, let alone designing IR LEDs into other systems.
In all of the applications discussed herein above, the limited magnitude of flux generated by the semiconductor emitter package has had a detrimental impact on the performance, design, size, weight, flexibility, cost, and other aspects of the devices in which they are employed. Consequently, much effort has been expended to develop higher intensity LEDs. Despite increases in luminous output that have been achieved as a result of these efforts, and despite all of the efforts expended to develop products that improve the performance of LEDs incorporated therein, high luminescent LEDs and the products that employ them suffer from high cost, high complexity, limited current capacity, and/or incompatibility with common manufacturing processes.
An exemplary application in an automotive environment wherein LEDs have imparted serious limitations on design and performance is a vehicle signal mirror. Signal mirrors generally employ one or more lamps in a mirror assembly to generate an information signal. In general, outside signal mirrors have employed a lamp assembly positioned either behind a dichroic mirror, such that the signal light passes through the mirror, or on the rearview mirror body housing, such that the signal lamp is independent of the mirror. Examples of such signal mirrors can be found in U.S. Pat. Nos. 5,361,190; 5,788,357; and 5,497,306. Even though signal mirrors incorporating LED signal lamps are gaining popularity, these mirrors have not yet received widespread acceptance. This limited acceptance may be due at least in part to the large volume, complexity, significant weight, and the high cost of implementing outside signal mirrors.
Outside rearview mirrors typically include a body housing mounted to the vehicle, a mirror assembly, and an adjustable support mechanism carrying the mirror assembly such that the driver can adjust the mirror angle. It is also common to provide other components in the mirror body housing such as one or more antennas (for accessories such as remote keyless entry), a motor for adjusting the mirror angle, and in some instances electronic circuitry. In direct conflict with this desire to provide a multitude of components in the outside rearview mirror body housing is the desire of vehicle designers to make the rearview mirrors as small and as aerodynamic as possible to minimize the mirror's impact on wind noise and vehicle styling. Consequently there is not a significant volume available within the mirror housing for additional components to be placed. In addition, it is desirable to make the weight of the mirror as light as possible to reduce vibration and its associated detrimental impact on rear vision. For these reasons, designers are presented with a significant challenge when attempting to design a signal mirror.
U.S. Pat. No. 5,361,190, entitled “MIRROR ASSEMBLY,” issued on Nov. 1, 1994, to John K. Roberts et al. illustrates an LED signal mirror. The 5,361,190 patent discloses a through-the-mirror signal indicator wherein a light source is positioned behind a dichroic mirror. The dichroic mirror passes light within a spectral band and attenuates light outside that spectral band. The light source positioned behind the dichroic mirror emits light in the spectral pass band of the dichroic mirror, such that a visual signal from the light source can be seen from the front of the mirror. However, the mirror will attenuate light which is not within the narrow pass band of the dichroic mirror. Although the ability to pass light through the entire area of the mirror is a significant advantage, there are several disadvantages to the dichroic signal mirrors that have restricted its commercial exploitation. These signal mirrors employ a large array of LEDs to generate the light signal. Such an LED array is heavy, necessitating substantial support structure for the rearview mirror, and costly. In addition, the LED array is large, requiring a large mirror body to accommodate the array, let alone the other mirror components of the mirror. Another significant disadvantage to dichroic mirrors is that they are expensive to manufacture, difficult to mass produce, and subject to performance variations as they age.
U.S. Pat. No. 5,788,357, entitled “MIRROR ASSEMBLY,” and issued to Muth et al. on Aug. 4, 1998, discloses a semitransparent mirror signal light assembly. The U.S. Pat. No. 5,788,357 describes efforts to overcome the inherent physical characteristics of earlier dichroic mirrors, such as the signal mirror disclosed in the U.S. Pat. No. 5,361,190. In particular, the U.S. Pat. No. 5,788,357 points out that the cost of producing dichroic mirrors is too high. Additionally, the U.S. Pat. No. 5,788,357 attempts to address the difficulties of providing a dichroic mirror with acceptable reflectivity and heat dissipation while maintaining adequate luminescence and a neutral chromatic appearance. In particular, the U.S. Pat. No. 5,788,357 employs a through-the-mirror arrangement using a semitransparent, non-dichroic mirror having a light source positioned behind it. The semitransparent mirror transmits about 1 percent to about 8 percent of a broad band of visible light. Like the U.S. Pat. No. 5,361,190, for LED signal lamps, the patent discloses a large bank of LEDs mounted on a substrate of relatively large dimension. Thus, the lamp array is heavy, requiring substantial structural support for the mirror, which will limit the types of applications in which the mirror can be used. In order to avoid the large LED array, the U.S. Pat. No. 5,788,357 teaches use of lamps other than LEDs.
U.S. Pat. No. 5,497,306, entitled “EXTERIOR VEHICLE SECURITY LIGHT,” issued on Mar. 5, 1996, to Todd Pastrick, discloses a signal mirror assembly including a lamp module mounted on the body housing of the exterior rearview mirror. The principle embodiment illustrates the difficulties encountered when attempting to accommodate an incandescent lamp. In particular the U.S. Pat. No. 5,497,306 shows a lamp housing assembly, which is removably attached to the exterior mirror body housing to facilitate replacement and maintenance of the signal lamp. Such an arrangement is costly, large, and restricts the designer's design flexibility. In addition, this design necessitates a redesign of the mirror housing to provide enough volume to accommodate the mirror, the removable light module, and any associated electronics. Enlarging the mirror housing is exactly what the auto manufacturers are trying to avoid.
These difficulties encountered when designing a signal mirror are representative of the types of problems encountered in many other components and assemblies employing LEDs. What is needed are components and assemblies producing brighter, stronger, and/or more easily discernible illumination and/or signals, and in many applications, such producing better illumination and/or signals in a compact volume.